23-CS-3 Sustainability, Engineering and the Environment · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2013 — 11-CS-3 Sustainability, Engineering and the Environment. Open book; non-communicating calculator permitted. Any four questions constitute a complete paper; all questions are of equal value (25 marks each).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Building in capacity or capability beyond what is needed wastes materials and energy over the product's life. Example: specifying a single oversized "one-size-fits-all" pump or motor for a range of duties means it runs inefficiently and consumes excess energy in most applications; instead, right-sizing the equipment to the actual duty (or using a variable-speed drive) prevents the continuous energy waste—and the associated power-plant emissions—that the oversized, over-capable design would cause. Similarly, packaging engineered far stronger than the product requires wastes material.
Designing a process to connect with the energy and material streams already available prevents waste. Example: a combined heat and power (cogeneration) plant that captures the waste heat from electricity generation and uses it for building or process heating, instead of rejecting it and burning additional fuel for heat. More broadly, industrial symbiosis—routing one plant's waste heat, steam, or by-product as the feedstock of a neighbouring plant—integrates flows so that what would be waste becomes a useful input, preventing both the disposal of the by-product and the extraction of virgin resources.
A product should last as long as its intended service life—no longer—so it does not persist as waste. Example: single-use packaging or cutlery made from a compostable/biodegradable material (such as PLA) rather than a permanent plastic: durable enough for its brief use, it then degrades harmlessly, preventing the persistent litter and landfill burden that an "immortal" plastic would create.
(i) Functional unit: the service delivered, e.g. "providing the reading material for one student's full course of study over the school's planning period (say, all textbooks read per student over several years)." This normalizes to equal educational service, since one e-reader displaces many printed books. (ii) Life-cycle stages: raw-material extraction; manufacturing/production; distribution and transport; use (including electricity for the e-reader, or none for a book); and end-of-life (recycling/disposal). (iii) Greatest impact by stage: in raw materials and manufacturing, the e-reader is worse per unit (mining of metals and rare earths, semiconductor fabrication, and a battery are energy- and toxics-intensive), whereas each printed book's manufacture (pulp, paper, ink) is smaller per unit but multiplied by many books; in use, the e-reader consumes electricity for charging while a book consumes none; in distribution, heavy paper books carry higher transport burdens; at end-of-life, the e-reader poses an e-waste/hazardous-materials problem while paper is recyclable/compostable. (iv) Stage of greatest impact for each: for the e-reader, the manufacturing (raw-material and electronics fabrication) stage dominates; for printed books, the raw-material/paper-production stage dominates. The overall comparison hinges on how many books one e-reader replaces and how long the device lasts—the more titles read per device, the more the e-reader's fixed manufacturing burden is justified.
Industrial ecology: the study and design of industrial systems modelled on natural ecosystems, in which the waste outputs of one process become the material or energy inputs of another, so that materials cycle and waste is minimized. Pollution prevention (P2): the strategy of reducing or eliminating waste and pollution at the source—through better design, material substitution, and process efficiency—rather than treating or disposing of it after it is created. Design for disassembly: designing products so they can be readily taken apart at end of life for repair, reuse, or material recovery.
